Synthetic fiber paper and method of making same



United States Pater 3,057,772 SYNTHETIC FIBER PAPER AND METHOD OF MAKING SAME Donald G. Magill, Jr., Milford, N.J., and James C. Eaton,

Doylestown, Pa., assigners to Riegel Paper Corporation, New York, N.Y., a corporation of Delaware N Drawing. Fiied Apr. '23, 1957, Ser. No. 654,440 3 Claims. ((11. 162-146) The present invention relates to paper products and methods of making them, and more particularly to an improved paper product comprising a very high percentage of synthetic fibers, such as glass or nylon, for example, and to a novel met-bod of making a new product of this type.

For certain uses of paper products, it is desirable to utilize synthetic fibers rather than conventional natural fibers. In many such cases, it is desirable to employ 100 percent synthetic fiber in the product. However, as a practical matter, it has been found that many synthetic fibers, and particularly hydrophobic synthetic fibers such as nylon, Orlon, etc., have little or no bonding proper-ties, and, by themselves (without the addition of undesirable solvents, etc.), will not form a web of sufficient wet strength to be lifted off the screen of a paper-making machine. Accordingly, it has been found necessary to utilize a mixture of natural and synthetic fibers, the natural fibers serving to bind the entire web together sufficiently to provide a useful product. For example, a mixture of 5 percent, by weight, of rope or rag fiber combined in a slurry with 95 percent nylon fiber, will form a web which can be removed effectively from an ordinary paper-making machine. purposes, even as much as 5 percent non-synthetic fiber renders the product objectionable. Accordingly, the present invention provides an improved synthetic paper product in which the content of non-synthetic fibers may be substantially reduced, to as little as 1 /2 percent, or less, in some cases.

The invention also provides a novel method of making the improved paper product, whereby a small percentage of natural or non-synthetic fibers may be incorporated effectively with a very high percentage of synthetic fibers to provide a paper product substantially approaching ideal characteristics, while having sufficient wet strength to be removed from a Fourdrinier wire in a conventional papermaking operation.

For a more complete understanding of the invention, reference should be made to the following detailed description, in conjunction with the following simplified flow diagram:

The new product incorporates a mixture of synthetic fibers, natural fibers and a precipitated binder. The synthetic fibers may be nylon, Orlon, or the like, while the natural fibers may be rope (Manila hemp), asbestos,

Water Pre are slur of hi hi beaten P W g y Natural fibers natural fibers Precipitating agent Add and precipitate binder,

Synthetic fibers 95% Natural fibers 1 However, for some.

ice

Water Dilute to paper stock consistency pH Adjust l Form web on paper Water machine or hast fibers, such as sisal, abaca, the foregoing not being limiting. The natural fibers are advantageously beaten to the point of false freeness. The binder is an emulsified, long-chain polymer, such as rubber, acrylic, or like material, advantageously having a lattice pattern; and by way of illustration and not of limitation, the following commercial materials have been found suitable: Rhoplex Bl5, a water emulsion of an acrylic resin, manufactured by Rohm & Haas; WA-35, now known as Lecton VM-5600, a water dispersion of a modified acrylic polymer, manufactured by E. I. du Pont de Nemours; Genton 110, a water dispersion of an alcohol soluble polyamide resin, manufactured by General Dispersions, Inc., Division of Belding Corticelli Industries; and Permaloid 170Vl20, a vinyl acetate copolymer modified to be alkali soluble, manufactured by Colloids, Inc.

In the preparation of the new paper product, it is important to prepare a slurry of the highly beaten natural fibers, without the synthetic fibers, and to precipitate onto to the natural fibers the binder agent utilized. The binder agent is in the form of an aqueous dispersion, which is precipitated onto the fibers in the slurry by the addition thereto of alum, aluminum chloride, or other precipitating agents, accompanied by steady agitation of the mixture. The precipitating agent should be added very slowly, and the agitation should be constant, in order to achieve the best results.

Into the slurry of natural fiber and binder there is added an amount in the order of 2%l0% alum or other precipitating agent to efiect precipitation of the binder onto the natural fibers. As a general rule, the relative amounts of binder and precipitating agent present in the slurry are such that the pH of the slurry falls within the range of 3.5 to 6.0. The exact pH value, of course, depends upon the particular binder and precipitating agent employed, and is also affected by the nature of the water used in the slurry. The primary consideration is, of course, that the proper amount of precipitating agent be added to the slurry to effect the desired precipitation.

Advantageously, the rope or other natural fiber may be present in the slurry in amounts up to 5%, it being understood that a minimum quantity of natural fiber is desirable. Binder is present in the slurry in amounts up to 15%, based upon the weight of the natural fiber; and suflicient water is used to constitute about of the slurry. The foregoing proportions may vary somewhat, of course, but the optimum quantities may be determined readily by laboratory tests.

After the slurry of natural fibers and binder has been prepared, the synthetic fibers are added and thoroughly mixed. The synthetic fiber may, for example, be glass, or a hydrophobic material, such as nylon or Orlon, in fiber lengths of about /s to /8 inch, and is advantageously pre-shrunk or stress relaxed, as more specifically set forth in the co-pending application Serial No. 97,412, filed March 22, 1961, which is owned by the assignee of this application. Although the /8 to inch synthetic fiber length is generally desired, such length is not, at present,

deemed critical, and lengths ranging from A to one inch may be used in appropriate cases. The thickness of the synthetic fibers is advantageously about 1 /2 to 3 denier per fiber.

After the mixture of fibers is thus prepared, it is properly diluted, the pH thereof is adjusted as necessary or desirable, and the stock is then flowed onto the screen of the paper machine, where most of the water is drawn through the screen by gravity and suction. The Web of fibers remaining on the wire or screen is adequately bonded together and may be removed from the wire and subjected to such further operations, such as pressing, smoothing, drying and calendering, as may be expedient. Depending upon the end use of the paper, an additional binding agent may be applied to the web during the processing thereof subsequent to its removal from the wire.

Tests made upon the new paper show that the synthetic fibers are predominantly on the side of the Web opposite the screen. This may be a desirable characteristic for many end uses of the paper.

The new paper product has many desirable and useful characteristics, and closely approaches the characteristics of a 100 percent synthetic fiber product. With the incorporation of a practical minimum of natural or nonsynthetic fiber, sufficient strength is imparted to the wet web to enable its removal from a Foundrinier wire for such subsequent processing thereof as may be desirable. Thus a practical and usable product has been prepared using as little as 1 /2 percent non-synthetic fiber.

One of the important features of the new product is the combination with a very high percentage of synthetic fiber of a very small percentage of natural fiber, highly beaten to a point of false freeness, onto which has been precipitated at suitable binder such as a rubber, acrylic or other emulsified, long-chain polymer. In this respect, it is pointed out that the binder cannot effectively be precipitated onto the synthetic fiber alone. However, when the binder is first precipitated onto the natural fibers, unexpected and advantageous characteristics are imparted to the product, permitting of a great reduction in the natural fiber content of the paper.

By way of example, the following comparative tables are indicative of the substantial improvement in the paper product realized by the precipitation of a binder onto beaten rope fibers, as compared to an equivalent product employing no binder.

Example 1 Synthetic Fiber: Nylon Natural Fiber: Rope Example 2 Synthetic Fiber: Nylon Natural Fiber: Rope Binder: 15% WA-35, 4% Alum It will be readily observed, from the foregoing tables, that substantial increases in tensile and tear strength result from the precipitation of binder onto the natural fibers.

Another important aspect of the invention resides in the novel method of preparing the new product, which includes preparing a natural fiber slurry and precipitating onto the natural fibers, before mixing thereof with the synthetic fibers, a suitable binding agent, which combines with the natural fibers in a manner such as to form a strong base for the synthetic fibers.

We claim:

1. The process of preparing stock for the manufacture of paper composed primarily of synthetic material, which comprises forming a slurry of highly beaten natural fibers, adding to the thus formed slurry an emulsified long-chain polymer binder, precipitating the binder onto the natural fibers by introducing into the mixture of slurry and binder from 2 percentto 10 percent of alum, accompanied by steady agitation of the mixture, to reduce the pH of the slurry to substantially within the range of 3.5 to 6.0, and thereafter mixing the natural fibers and precipitated binder together with hydrophobic synthetic fibers in an aqueous solution in the proportion of less than 5 percent natural fibers and more than percent synthetic fibers.

2. The process of preparing stock for the manufacture of paper composed primarily of hydrophobic synthetic fibers, which comprises the steps of, preparing an aqueous slurry of highly beaten natural fibers, introducing into the slurry an emulsified long-chain polymer binder, precipitating the binder onto the natural fibers in the slurry, and thereafter mixing hydrophobic synthetic fibers in the slurry of natural fibers in a proportion of 95 to 98 /2 percent synthetic fibers to 5 to 1 /2 percent natural fibers.

3. The process of claim 2, in which said natural fibers are beaten to the point of false freeness prior to the preparation of said slurry.

References Cited in the file of this patent UNITED STATES PATENTS 2,357,392 Francis Sept. 5, 1944 2,477,000 Osborne July 26, 1949 2,504,744 Sproull et a1. -1- Apr. 18, 1950 2,526,125 Francis Oct. 17, 1950 2,633,433 Hollenberg Mar. 31, 1953 2,653,870 Kast Sept. 29, 1953 2,666,699 McQuiston et al. Jan. 19, 1954 2,721,139 Arledter Oct. 18, 1955 2,807,543 McQuiston Sept. 24, 1957 2,930,106 Wrotnowski Mar. 29, 1960 

1. THE PROCESS OF PREPARING STOCK FOR THE MANUFACTURE OF PAPER COMPOSED PRIMARILY OF SYNTHETIC MATERIAL, WHICH COMPRISES FORMING A SLURRY OF HIGHLYBEATAEN NATURAL FIBERS, ADDING TO THE THUS FORMED SLURRY AN EMULSIFIED LONG-CHAIN POLYMER BINDER, RECIPITATING THE BINDER ONTO THE NATURAL FIBERS BY INTRODUCING INTO THE MIXTURE OF SLURRY AND BINDER FROM 2 PERCENT TO 10 PERCENT OF ALUM, ACCOMPANIED BY STEADY AGITATION OF THE MIXTURE, TO REDUCE THE PH OF THE SLURRY TO SUBSTANTIALLY WITHIN THE RANGE OF 3.5 TO 6.0, AND THEREAFTER MIXING THE NATURAL FIBERS AND PRECIPITATED BINDER TOGETHER WITH HYDROPHOBIC SYNTHETIC FIBERS IN AN AQUEOUS SOLUTION IN THE PROPORTION OF LESS THAN 5 PERCENT NATURAL FIBERS AND MORE THAN 95 PERCENT SYNTHETIC FIBERS. 